In the long-term viewpoint, the development of environmentally friendly and sustainable energy sources has been attracting considerable attention world-wide. Generally-used fossil fuels emit a large amount of carbon dioxide, thus causing global warming. Global warming leads to various weather anomalies and ecosystem variations derived from sea level rise, and thus it is necessary to develop clean energy sources emitting no carbon dioxide.
A fuel cell, which is a device for producing electric energy using a chemical reaction in which fuel is oxidized at an anode and oxygen is reduced at a cathode, has actively been researched as a next-generation clean energy source. A direct methanol fuel cell, which is one of the low-temperature type fuel cells applicable for various mobile appliances, uses methanol as fuel. In the direct methanol fuel cell, a platinum catalyst is used in order to accelerate the oxidation reaction of methanol at an anode.
Currently, a catalyst in which carbon is supported with platinum-ruthenium alloy nanoparticles of 2˜4 nanometers is most widely used as an anode catalyst. Methanol is adsorbed onto platinum nanoparticles in the form of carbon monoxide at the anode, oxidized into carbon dioxide, and then detached from the anode. Here, carbon monoxide causes a platinum poisoning phenomenon in which the active sites of platinum nanoparticles are blocked by carbon monoxide to reduce the activity thereof because the bonding force of carbon monoxide to platinum is very strong. Ruthenium serves to remarkably reduce the platinum poisoning phenomenon because it functions to rapidly oxidize carbon monoxide adsorbed on platinum into carbon dioxide. However, such an anode catalyst is problematic in that its catalytic activity is deteriorated with the passage of time because carbon, used as a carrier, is corroded under a DFMC operation environment to cause the agglomeration and elution of nanoparticles.
In order to solve the above problems of an anode catalyst, methods of preventing the poisoning of a platinum catalyst by accelerating the oxidation of adsorbed carbon monoxide while using a metal oxide having excellent durability as a carrier have been proposed. In particular, tungsten oxide, such as WO3, has been attracting considerable attention as a carrier capable of replacing carbon because it has strong resistance to carbon monoxide poisoning by accelerating the oxidation of carbon monoxide adsorbed with an OH group and has high durability under a DFMC operation environment. However, such carriers are problematic in that they are not suitable for use in DMFCs because they have a small surface area and do not have electrical conductivity. For this reason, it is still required to develop a novel catalyst having strong resistance to carbon monoxide poisoning, having high durability under a DFMC operation environment and having a large surface area to exhibit excellent activity.